The present invention relates to a method and a corresponding device for monitoring a state of at least one battery cell of a battery having a number of series-connected or series-connectable battery cells.
In battery cells, faults may occur. These faults can be, for example, local short circuits which are caused, for example, by dendrites and/or contamination in the battery cells, aging of the battery cells, production faults or mechanical effects. Such short circuits can lead to a production of self-discharging currents in the battery cells. In consequence, these faults represent a safety risk in a charged state of a battery having such battery cells since local heating of the battery cells may occur.
Current battery systems which are typically used for electromobility applications comprise batteries having a number of series-connected or connectable battery cells through which one and the same current flows during charging and/or discharging of the battery. The electrical energy and power which can be taken from such a battery system is determined by the battery cell which has a minimum capacity and a maximum internal impedance of all battery cells. It is advantageous, therefore, that in such a battery system, battery cells are installed which have similar capacities and internal impedances, if possible. It is known that aging of a battery cell typically reduces its capacity and typically increases its internal impedance. Due to aging and self discharging currents flowing in the battery cells of an aforementioned battery system, the battery cells discharge at different rates. In the long term, this leads to different charging states of the battery cells. It is necessary, therefore, to perform a charging state compensation between the charging state of the battery cells of such a battery system regularly. This process is usually called balancing.
From document CN 10231546 B, a battery having a number of battery cells is known. In this context, a state of the battery is monitored by a battery management system. The battery management system is designed to initiate and activate a performance of a charging state compensation between different charging states of the battery cells of the battery.
From document US 2013/0018606, a battery having a number of battery cells is known. In this context, a number of charging state compensations are performed between different charging states of the battery cells of the battery. Furthermore, a frequency is determined for each battery cell with which an energy stored in the respective battery cell is varied during the number of charging state compensations. Using an evaluation of the frequency determined for each battery cell, it is determined whether the respective battery cell is in a faulty state. Such a faulty state can occur in consequence of an internal short circuit of the respective battery cell.